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Classification and fertility status of soils on slopes of varying orientations in Umuahia area of Abia
State, Nigeria
ARTICLE INFO
ARTICLE INFO
Article history:
Received March 20, 2020
Received in revised form March 29, 2020
Accepted April 12, 2020
Available online May 20 2020
ABSTRACT
The slope orientation and position of toposequence influence soil properties
along the landscape. The study classified and evaluated the fertility status of soils
on slopes of varying orientations in Umudike (East-lying Toposequence) and Itu
(West-lying Toposequence) located in Olokoro Umuahia, Abia State southeastern
Nigeria. Transect soil sampling technique was employed in locating 3 distinct top
units (Summit, Midslope and Footslope) along each of the toposequence. Soil
profile pit was dug at each top unit, described using FAO guidelines and sampled
according to genetic horizons. Soil samples collected were subjected to routine
laboratory analyses. Pedons were classified using the USDA Soil Taxonomy Sys-
tem and correlated with World Reference Base while the fertility status was eval-
uated using elemental ratios. The results indicated that soils of the two
toposequence were dominated by sandy clay loam texture. Consistency of the
pedons generally varied from very friable (Vfr) to very firm (Vfi) in the two
toposequence. Soil pH was very strongly acidic (4.58-4.78) in the east lying
toposequence but varied from very strongly acidic to strongly acidic (4.52-5.30)
in the west lying toposequence. Organic matter concentration was higher at the
epipedons and ranged from 26.44 to 23.36 g kg -1 and 18.9 to 30.64 g kg -1 in soils
of east-lying and west-lying slopes, respectively. K: Mg ratio varied from 0.01-
0.12 and 0.01-0.08 at the east and west lying slopes, respectively. The pedons of
the summit, midslope and footslope were as classified Grossarenic Paleudalfs,
Typic Paleudalfs and Arenic Hapludalfs for respectively for the east-lying slope
and Arenic Glossudalfs, Typic Paleudalfs and Typic Ferrudalfs, respectively for
the west-lying slope. Generally, the two toposequences were of poor fertility sta-
tus.
Keywords:
Toposequence
Slope orientation
Soil properties
Soil fertility
Soil classification
Corresponding Author’s E-mail Address:
[email protected] .+2348037687630
https://doi.org/10.36265/njss.2020.300114
ISSN-1597-4488 © Publishing Realtime.
All right reserved.
Aliba et al. NJSS 30 (1) 2020 111-123
Department of Soil Science and Technology, Federal University of Technology, Owerri
1.0. Introduction
Soils differ in their characteristics primarily because of
topography (Aduloju and Tetengi, 2011). According to
Mulla and McBratney (2001), variability in soil properties
at the series level is often caused by small changes in to-
pography that affect the transport and storage of water
across and within the soil profile.
The topography is a significant factor which controls most
surface processes taking place on earth (soil formation and
soil development). Topography has an influence on soil
chemical and physical properties and also on the pattern of
soil distribution over the landscape (Kalivas et al., 2002;
Esu et al., 2008). One reason for variation in soil proper-
ties with topographic settings is the orientation of hill
slopes on which soils develop, and this affects the micro-
climate, as in north versus south-facing slopes, (Iqbal et
al., 2004). Slope aspect has been shown to affect the tem-
perature of the soil, vegetation establishment, and moisture
levels. These factors, in turn, can affect the distribution of
soil organic matter, the presence or absence of an E hori-
zon (in more humid areas), pH, and nutrient levels
(Birkeland, 1984). North facing slopes generally have less
sunlight because of its higher moisture levels and greater
vegetation establishment resulting in more organic matter.
Soil pH trends and nutrient levels are usually associated
Aliba, V.O., Onweremadu E.U., Aririguzo, B. N. and Okoli, N. H.
112
with vegetation and can also be affected by the slope as-
pect. Mesic vegetation types are usually found on the
North facing slopes, while more xeric vegetation is found
on the south-facing slopes (Birkeland 1984).
The study and understanding of soil properties and their
distribution over an area has proved useful for the devel-
opment of soil management plan for efficient utilization of
limited soil resources and agrotechnology transfer (Buol et
al., 2003). In Nigeria, many works on the relationship be-
tween landscape positions and soil properties were docu-
mented (Annan-Afful et al., 2004; Abe et al., 2009). For
instance, Ogban et al. (1999) deduced that nutrient status
and soil properties are related to the topography of the
land area. Also, Osodeke et al. (2005) reported differences
in quantity and forms of sesquioxides as influenced by
geomorphic positions. They observed that the soils of the
profiles at higher slopes were dominated by the crystalline
forms of iron (Fe) and aluminium (Al)-oxides while the
soils of the valley bottom were dominated by the amor-
phous forms of Fe and Al. Elsewhere, Osodeke and Oson-
du (2006) observed a wide variation in phosphorus (P)
distribution along a toposequence in southeastern Nigeria
where highest total P was observed at the upper slope
while the lowest value was noted at the middle slope.
With the emphasis being shifted to precision farming in
Nigeria to meet up food requirement of a rapidly growing
population, investigations on properties of soils on differ-
ent landscape positions are necessary. Potentials of soils
can readily be tapped when information on its physical,
chemical and biological properties are available. It will
also be equally essential to classify the soils using their
inherent characteristics. In a manner that will ease commu-
nication and transfer of knowledge about such soils to
farmers, stakeholders and soil scientists since soil data are
primarily needed as a first step in sustainable land use and
soil management decisions (Chukwu, 2013). Non-use of
soil survey data has resulted in soil and soil-related envi-
ronmental problems like nutrient depletion (Onweremadu,
2006) compaction, flooding, and reduced yield (Zinck,
1990).
Olokoro Umuahia is an agrarian state; its dwellers are
mainly commercial farmers of both small scale and large
scale production of several staple crops such as cassava,
yam, maize and tree crops like oil palm among others are
their primary produce. There is limited data on soils of this
area. Previously, Nuga et al. (2006) classified soils along a
toposequence in this area without considering the orienta-
tion of the slope. Slope orientation is vital in the develop-
ment of soils, but the position of soil on a slope has also
been found to affect the properties of soil. In light of the
above, it is of paramount importance to have in-depth
knowledge on the characteristics and taxonomical classifi-
cation of soils on varying slope orientations and positions,
to manage and use the resources based on their potentials
and limitations and thereby maximize crop production to
the allowable genetic potential limits and conserve the
soils for future use. Therefore the primary objective of the
study was to classify and evaluate the fertility of soils on
slopes of varying orientation in Olokoro Umuahia South-
eastern Nigeria using USDA Soil Taxonomy System and
correlate with the World Reference Base.
2.0. Materials and methods
2.1. Description of the Study Area
Two locations, Itu and Umudike in Olokoro Umuahia
Abia State, southeastern Nigeria with toposequence of
varying orientations (East lying and west lying) were used
for the study. Olokoro Umuahia lies between Latitudes 5°
26'N and 5°37'N; and Longitudes 7°23'E and 7°36'E. Soils
of the study area were derived from Coastal Plain Sand
(Benin formation) (Orajaka, 1975). The area lies within
the lowland and plain areas of southeastern Nigeria geo-
morphology with the primary hydrologic resource of the
area being the Imo River and its tributaries. The study area
is characterized by a humid tropical climate with two sea-
sons, namely, the wet and dry seasons (Obi, 1982). The
relative humidity is high (above 80%) especially during
the wet season with an average annual rainfall of about
2500 mm while annual temperature varies from 260C to
310C (NIMET, 2008). The predominant vegetation in the
area is tropical rainforest. Gmelina arborea is the dominant
plant occupying about one half of the area of the forest
reserve while Tectona Grandis is the secondary dominant
tree plant. However, secondary forest dominates the area
due to anthropogenic activities. The significant socio-
economic activity in the area is farming, with about 70%
of the total land area under crop cultivation. Commonly
cultivated crops include maize, cassava and yam.
2.2. Detailed Field Work and Soil Sampling
Transect soil survey technique was used in field sampling.
With the aid of a compass, east lying and west lying slopes
were located in Umudike and Itu, respectively. Guided by
transect sampling technique, one profile pit was sunk each
in the summit, midslope and footslope of the Umudike east
-lying and Itu-west toposequencies. Hence, a total of six
(6) profile pits were used in the study. All soil profiles
were georeferenced using a handheld Global Positioning
System (GPS) Receiver (Garmin Ltd, USA). The profile
pits were described using FAO (1998) guidelines, and soil
samples were collected according to horizon differentia-
tion. Undisturbed soil samples for determination of bulk
density were also collected using core samplers. The soil
samples collected were air-dried, crushed and sieved
through a 2 mm sieve. Also, the soils used for organic
matter and total nitrogen determinations were further
ground to pass through 0.5 mm mesh.
2.3. Laboratory Analyses
Particle size distribution was determined by the hydrome-
ter method of Gee and Or (2002), Soil bulk density was
determined by the core sampler method, Silt/clay ratio was
determined by dividing the value of silt with clay value
while soil pH was measured using glass electrode pH me-
ter (Thomas, 1996). Exchangeable bases (Ca, Mg, K and
Na) were extracted using 1NNH4OAc buffered at pH 7.
Calcium and magnesium were then determined by com-
plexometric titration method (Thomas 1982) while potassi-
um and sodium were read on the flame photometer. Total
nitrogen was determined by the Macro Kjeldahl method
(Bremner and Mulvaney, 1996), Organic carbon was ob-
Classification and fertility status of soils on slopes of varying orientations
113
Figure 1: Location map of the study area
Table 1: Geographical coordinates of the sampled sites
Site Topounit Slope Latitude (N)
(o)
Longitude (E)
(o)
Elevation
(M)
Itu (WLT) Crest 5.7º 5º28'.844'' 7º31'.352'' 143
Itu (WLT) Midslope 6.8º 5º28'.844'' 7º31'.304'' 142
Itu (WLT) Footslope 5.2º 5º28'.804'' 7º31'.265'' 135
Umudike (ELT) Crest 5.0º 5º28'.914'' 7º31'.395'' 141
Umudike (ELT) Midslope 7.2º 5º28'.546'' 7º31'.414'' 138
Umudike (ELT) Footslope 7.9º 5º28'.983'' 7º31'.458'' 121
WLT = West-Lying Toposequence, ELT = East-Lying Toposequence
Aliba et al. NJSS 30 (1) 2020 111-123
114
tained by chromic wet oxidation method (Nelson and
Sommers, 1996) and organic matter derived by multiply-
ing with the Van Bemmelen's factor while cation exchange
capacity was determined by NH4OAc saturation method
(Udo et al., 2009). Ca: Mg ratio was obtained by the div-
ing value of exchangeable Ca with a value of exchangea-
ble Mg. Similarly, the K: Mg ratio was obtained by divid-
ing the value of exchangeable K with a value of exchange-
able Mg. Total exchangeable acidity was extracted with
IM KCl and then titrated with 0.01M NaOH (Udo et al.,
2009) while percentage base saturation was calculated as
the proportion of exchangeable complex occupied by ex-
changeable bases.
2.4. Soil Classification
The data obtained from the field study and Laboratory
analyses were used to classify the pedons according to the
USDA Soil Taxonomy System (Soil Survey Staff, 2010)
and then correlated with World Reference Base for Re-
sources (IUSS Working Group WRB, 2010).
2.5. Statistical Analysis
Data generated were subjected to coefficient of variation
and variation ranked according to the procedure of Wild-
ing et al. (1994) where CV < 15% = least variation, CV
>15 < 35% = moderate variation, CV > 35 <100% = high
variation.
3.0. Results and Discussion
3.1. Soil Morphological Properties
Results of the morphological properties of both
toposequences studied are presented in Tables 2 and 3. It
was observed that regardless of the slope orientation, the
soils were generally shallow at all the slope positions. At
Umudike east-lying slope, the soil depth varied from 0-
130 cm, 0-150 cm and 0-150 cm for the summit, midslope
and footslope, respectively (Table 2). In contrast, at Itu
west-lying slope, it ranged from 0-120 cm, 0-110 cm and 0
-180 cm in the summit, midslope and footslope, respec-
tively (Table 3). However, generally, the soils had similar
horizon pattern of A, AB, Bt1, Bt2 and Bt3 except for
Umudike summit that had BA as the third horizon.
Soil colour is probably the most important feature to as-
sess the soil moisture required in landscape (Peter Schmitt
et al., 1996). Soil colour of Umudike east-lying slope var-
ied from very dark greyish brown (10YR3/2) moist at A
horizon of summit soil position, while strong brown
(7.5YR5/8) moist was observed at the Bt3 horizon. The
greyish colour of A and AB horizons may be attributed to
poor internal drainage condition (Esu, 2010). At the mid-
slope of Umudike toposequence, dark brown (7.5YR3/2)
moist colour was recorded at the A-horizon. At the same
time, it had strong brown (7.5YR5/8) moist colour at the
Bt3 horizon whereas, dark grey (5YR4/1) moist and red-
dish yellow (7.5YR6/8) colour characterized A horizon
and Bt3 horizon of Umudike footslope, respectively (Table
2). On the other hand, the summit of Itu west lying slope
was characterized by brown (7.5YR4/2) moist and yellow-
ish red (5YR5/6) moist colour at the A and Bt3 horizons,
respectively. In contrast, at the midslope, very dark grey
(7.5YR3/1) moist and yellowish red (5YR3/2) moist char-
acterized the upper and bottom horizons, respectively.
Very dark greyish brown (10YR3/2) moist and reddish
yellow (5YR6/6) moist colour dominated A and Bt3 hori-
zons respectively of this footslope (Table 3).
The topsoil of Umudike east-lying slope was fine crumb at
the summit and midslope while at footslope, the very
coarse blocky structure was observed. In contrast, at the
Itu west-lying slope very fine gravel was observed for
summit and midslope but very coarse blocky for the foot-
slope. However, soil structure was fine crumb, very coarse
blocky and medium crumb at the lower horizon of the
summit, midslope and foot slope of Umudike east-lying
slope, respectively. On the other hand, lower horizons of
Itu west-lying slope were fine crumb, blocky crumb and
very crumb angular blocky at the summit, midslope and
footslope, respectively (Tables 2 and 3).
Expectedly, roots and faunal activity was generally ob-
served to be in abundance in the epipedons of both the
west and east lying toposequence However, while very
few roots and faunal activity was observed at the lower
horizon of the midslope and footslope, few roots and fau-
nal activity was recorded at the summit of Umudike slope
(Table 2). At Itu west-lying slope, abundance and very few
roots and faunal activity were recorded in the epipedon
and lower horizon of summit and footslope, respectively.
In contrast, at the midslope, an abundance of roots and
faunal activity was recorded at the A horizon. In contrast,
there was an absence of roots and faunal activity at the
lower horizon.
Consistency of the soils generally varied from very friable
(Vfr) to very firm (Vfi) at the soil position irrespective of
toposequence (Tables 2 and 3). The observed difference in
soil consistency could probably be as a result of variation
in particle size distribution, particularly clay content and
also the nature of the clay particles. Moradi (2013) had
earlier asserted that soil consistency varies with soil tex-
ture. At the Umudike east-lying toposequence, clear
smooth (cs) dominated epipedon of the top units while the
diffuse smooth (Ds) boundary dominated the sub-soil hori-
zons (Table 2). A similar trend of boundary pattern was
also observed in Itu toposequence except for the footslope,
where the opposite trend was recorded (Table 3). The vari-
ations like the horizon boundaries may indicate the exist-
ence of variations in processes that have formed the soils
(Cools and De Vos, 2010).
3.2. Soil Physical Properties of the East and West Lying
Slopes
Results of the selected soil physical properties of Umudike
east-lying toposequence and Itu west-lying toposequence
are shown in Tables 4 and 5, respectively. At the Umudike
east-lying toposequence, sand particles varied from 764-
618 g kg -1, 724-418 g kg -1, and 664-504 g kg -1 for the
summit, midslope and footslope respectively (Table 4),
whereas at the Itu West-lying slope, sand particles ranged
from 724-604 g kg -1, 684-524 g kg -1 and 604-564 g kg -1
at the summit midslope and footslope, respectively (Table
5). Generally, the sand particle slightly decreased with
depth in both toposequences. Except for the summit of the
Classification and fertility status of soils on slopes of varying orientations
115
Horizon Depth
(cm)
Colour (moist) Structure Consistence
(moist)
Roots Faunal ac-
tivity
Boundary
Umudike East-lying summit (Grossarenic Paleudalfs)
A 0-5 Very dark greyish
brown 10YR3/2
0, cr, f Vfr Abt Abt Ds
AB 5-23 dark grayish brown
10YR4/2
3, abk, vc Fr Abt Abt Cs
Bt1 23-56 Brown 7.5YR4/4 2, cr, m Fi M M Ds
Bt2 56-95 Reddish brown
5YR5/4
Fi F F Ds
Bt3 95-130 Strong brown
7.5YR5/8
0, cr, f Vfi F F Ds
Umudike East-lying midslope (Typic Paleudalfs)
A 0-7 Dark brown
7.5YR3/2
0, cr, f Vfr Abt Abt Cs
AB 7-37 brown 7.5YR4/2 3, bk, c Fr M M Cs
Bt1 37-66 brown 7.5YR5/4 2, cr, m Fi M M Ds
Bt2 66-100 Reddish yellow
7.5YR6/6
0, cr, f Fi F F Ds
Bt3 100-150 Strong brown
7.5YR5/8
3, bk, c Vfi Vf Vf Ds
Umudike East-lying footslope (Arenic Hapludalfs)
A 0-7 Dark gray 5YR4/1 3, bk, vc Vfr Abt Abt Cs
AB 7-20 brown 7.5YR4/3 0, cr, f Fr M M Cs
Bt1 20-52 Light reddish brown
5YR6/4
0, cr, f Fi M M Ds
Bt2 52-98 Reddish yellow
7.5YR6/6
0, cr, f Fi F F Ds
Bt3 98-150 Reddish yellow
7.5YR6/8
2, cr, m Vfi Vf Vf Ds
Table 2: Morphological properties of the Umudike east-lying toposequence
Key: 0=structuress, 1=weak, 2=moderate, 3=strong, cr= crumb, m =medium, abk=angular blocky, bk=blocky, vc=very coarse, f =fine, sbk
=subangular blocky, gr=granular, c = coarse, mFr =moderately friable, Vfi= very firm, Vfr= very friable, fr= friable, Abt=abundant, f= few ,
Vf=very few, Cs=clear smooth, Ds = diffuse smooth.
Umudike East-lying slope where low (CV ≤ 15%) varia-
bility in the distribution of sand, particles were observed,
other topo units recorded medium (CV ≥ 15 ≤ 35%) varia-
bility. However, low variability was recorded for all the
pedons of Itu west-lying slope in the distribution of sand
particle size, which indicated homogeneity of this soil
property.
For silt particle size, mean values of 62 g kg -1, 63.6 g kg -
1 and 66 g kg-1 were recorded for the summit, midslope
and footslope, respectively at the Umudike east-lying
toposequence. In contrast, at the Itu west lying
toposequence, mean values of 82 g kg -1, 126 g kg -1 and
102 g kg -1 were noted for the summit, midslope and foot-
slope, respectively. Generally, regardless of slope orienta-
tion, the results indicated a decrease in silt content with
depth and high variation (CV > 35%) in the distribution of
silt in all the pedons studied. Clay particles did not follow
similar distribution trend with sand, and silt particles in the
pedons as the values increased with soil depth in all the
pedons studied which may be due to the illuviation pedo-
genic processes that might have taken place within the
pedons. For the Umudike east lying toposequence, the
highest mean value of 345.6 g kg -1 was recorded in the
midslope while for the Itu west lying slope, the highest
mean value of 306 g kg -1 was observed in the footslope.
In general, sand particles dominated the mineral matter in
all the topo units studied which may be partly attributed to
the dominance of quartz in the coastal plain sands parent
material from which the soils were derived (Obi, 2015).
Part may be due to geological processes involving sorting
of soil materials by biological activities, clay migration
through eluviation and illuviation, or surface erosion by
runoff or their combination (Akinbola et al., 2009). Tex-
ture varied from sandy loam to sandy clay loam, sandy
loam to clay and sandy loam to sandy clay at the Umudike
east lying summit, midslope and footslope, respectively
while at the Itu west lying toposequence, texture varied
from sandy loam to sandy clay loam for the summit and
midslope. In contrast, in the foot slope, it varied from
sandy loam to sandy clay. Silt Clay Ratio (SCR) of the
soils followed a similar decreasing trend with clay. It
ranged from 0.93-0.04 and 0.7-0.04 in the summit of the
two toposequences, 1.26-0.04 and 1.59-0.27 in the mid-
slope whereas in the floor slope, it varied from 0.66-0.04
and 1.08-0.14 in the East and West Lying Slopes respec-
tively. Silt to clay ratios has been used to study the degree
of pedogenic weathering in soils (Sombroek and Zonne-
veld, 1971). Generally, low values (< 0.75) indicate old
age of soils; values between 0.75 and 1.5 indicate moder-
ate pedogenic weathering processes, while high values
(>1.5) indicate recent pedogenic processes (Sombroek and
Aliba et al. NJSS 30 (1) 2020 111-123
116
Table 3: Morphological properties of the Itu west-lying slope
Key: 0=structuress, 1=weak, 2=moderate, 3=strong, cr= crumb, m =medium, abk=angular blocky, bk=blocky, vc=very coarse, f =fine, sbk
=subangular blocky, gr=granular, c = coarse, mFr =moderately friable, mVfi= moderately very firm, Vfr= very friable, fr= friable, Abt=abundant,
f= few , Vf=very few, Cs=clear smooth, Ds = diffuse smooth.
Horizon Depth (cm) Colour (moist) Structure Consistence
(moist)
Roots Faunal
activity
Boundary
Itu West-lying summit (Arenic Glossudalfs)
A 0-6 Brown 7.5YR4/2 0, gr, Vf Vfr Abt Abt Cs
AB 6-38 Brown 7.5YR5/2 0, gr, f Fr M M Cs
Bt1 38-83 Strong brown
7.5YR4/6
1, cr, m Fi F F Ds
Bt2 83-106 Strong brown
7.5YR5/6
1, cr, f Vfi Vf Vf Ds
Bt3 106-120 Yellowish red
5YR5/6
1, cr, f Vfi Vf Vf Ds
Itu West-lying midslope (Typic Paleudalfs)
A 0-7 Very dark grey
7.5YR3/1
0, gr, Vf Fr Abt Abt Cs
AB 7-26 brown 7.5YR4/3 0, gr, f Fi M M Cs
Bt1 26-50 Yellowish red
5YR4/6
3, bk, c Fi F F Ds
Bt2 50-73 Yellowish red
5YR5/6
2, cr, m Vfi Ab Ab Ds
Bt3 73-110 Yellowish red
5YR5/8
3, bk, c Vfi Ab Ab Ds
Itu West-lying footslope (Typic Ferrudalfs)
A 0-8 Very dark greyish
brown 10YR3/2
3, abk, vc Vfr Abt Abt Ds
AB 8-29 Dark brown
7.5YR3/2
3, sbk, vc Fr M M Ds
Bt1 29-86 Dark brown
7.5YR3/2
3, bk, c Fi F F Cs
Bt2 86-110 Reddish yellow
5YR6/6
3, bk, vc Vfi Vf Vf Cs
Bt3 110-180 Reddish yellow
5YR6/6
3, abk, vc Vfi Vf Vf Cs
Zonneveld, 1971). Therefore, the mean values of SCR of
the present study revealed old age of soils of both
toposequences which may be due to high temperature and
annual rainfall prevalent in the study area which probably
encourages rapid weathering. However, high (CV > 35%)
variability of SCR in the study indicated non-homogeneity
of SCR distribution.
Mean bulk density ranged from 1.37-1.32gcm-3 in the west
lying toposequence while it varied from 1.36-1.32g cm-3 in
the east lying toposequence (Tables 4 and 5). Mean values
of BD recorded in the study were below the critical mini-
mum value of 1.5g cm-3 for root compaction, thus, ade-
quate for crop production. Bulk density (BD) of the soils
of the different slope orientations generally increased with
depth. Increase in bulk density with depth could be at-
tributed to a decrease in organic matter accumulation with
depth, less root penetration and compaction caused by the
weight of the overlying layers (Brady and Weil, 2004).
3.3. Soil Chemical Properties of the East and West Lying
Slopes
Selected soil chemical properties of the two toposequenc-
es studied are shown in Table 6 and 7. The results revealed
that the soils were generally acidic, which slightly in-
creased with depth in the top units except for the summit
of Itu west-lying slope. In the east lying toposequence, the
highest value of 4.78 was recorded in midslope followed
by 4.64 in the summit and 4.58 in the footslope. However,
in the west lying toposequence, soil pH decreased with
decreasing slope percentage. The highest value of 5.3 and
the lowest value of 4.52 were recorded in summit and
footslope, respectively. Generally, the pH of the two
slopes lying in different positions varied from extremely
acidic to moderately acidic (FAO, 2004). The low (CV
≤15%) variability observed in the distribution of pH in
both toposequences, indicated uniformity of this property
irrespective of the top units and orientation of the slopes.
Organic matter contents of the soils were generally low
and decreased with depth in both toposequences. Highest
mean values of 26.44 and 30.64 g kg-1 were observed in
the midslopes of the east and west lying slopes, respective-
ly. In contrast, the lowest mean values of 23.26 and 18.9 g
kg-s1 were recorded in the summit of east and west
toposequences, respectively (Table 6 and 7). The low or-
ganic matter recorded in the study could be attributed to
high rate of mineralization of organic matter in the soils
Classification and fertility status of soils on slopes of varying orientations
117
Horizon Depth
(cm)
Sand
(g kg-1)
Silt
(g kg-1)
Clay
(g kg-1)
TC SCR BD
(g cm-3)
Umudike East-Lying Summit (Grossarenic Paleudalfs)
A 0-5 764 114 122 SL 0.93 1.23
AB 5-23 664 94 242 SCL 0.39 1.26
Bt1 23-56 618 54 328 SCL 0.16 1.33
Bt2 56-95 664 14 322 SCL 0.04 1.44
Bt3 95-130 624 34 342 SCL 0.1 1.54
Mean 666.8 62 271.2 0.324 1.36
CV 8.769 66.89 33.96 112.28 9.49
Umudike East-Lying Midslope ( Typic Paleudalfs)
A 0-7 724 122 154 SL 1.26 1.21
AB 7-37 644 114 242 SCL 0.47 1.24
Bt1 37-66 604 14 382 SC 0.04 1.26
Bt2 66-100 418 34 548 C 0.06 1.41
Bt3 100-150 564 34 402 SC 0.08 1.49
Mean 590.8 63.6 345.6 0.382 1.32
CV 19.17 78.68 48.89 136.68 9.19
Umudike East-Lying Footslope (Arenic Hapludalfs)
A 0-7 664 94 242 SL 0.66 1.19
AB 7-20 604 54 342 SCL 0.16 1.25
Bt1 20-52 604 14 382 SC 0.04 1.39
Bt2 52-98 504 54 442 SC 0.12 1.41
Bt3 98-150 504 114 382 SC 0.3 1.47
Mean 576 66 358 0.26 1.34
CV 17.25 59.07 36.11 95.59 8.73
Table 4:Physical properties of the Umudike east-lying toposequence
Key: TC=textural class, S=sand, SL=sandy loam, SCL=sandy clay loamy, SC= sandy clay, BD=bulk density.
Table 5: Physical properties of the Itu west-lying toposequence
Key: TC=textural class, SL=sandy loam, SCL=sandy clay loamy, SC= sandy clay, BD=bulk density.
Horizon Depth
(cm)
Sand
(g kg-1)
Silt
(g kg-1)
Clay
(g kg-1)
TC SCR BD
(g cm-3)
Itu West-Lying Summit (Arenic Glossudalfs)
A 0-6 724 114 162 SL 0.7 1.21
AB 6-38 624 134 242 SCL 0.55 1.29
Bt1 38-83 604 114 282 SCL 0.4 1.37
Bt2 83-106 638 14 348 SCL 0.04 1.48
Bt3 106-120 724 34 242 SCL 0.14 1.51
Mean 662.8 82 255.2 0.37 1.37
CV 49.103 61.50 51.27 237.98 119.44
Itu West-Lying Midslope (Typic Paleudalfs)
A 0-7 684 94 222 SL 1.59 1.19
AB 7-Jul 564 194 242 SCL 0.8 1.23
Bt1 26-50 564 114 322 SCL 0.35 1.29
Bt2 50-73 564 94 342 SCL 0.27 1.46
Bt3 73-110 524 134 342 SCL 0.39 1.5
Mean 580 126 294 0.68 1.33
CV 10.46 27.21 36.99 80.67 10.40
Itu West-Lying Footslope (Typic Ferrudalfs)
A 0-8 604 154 242 SL 1.08 1.17
AB 8-29 664 154 182 SL 0.85 1.24
BA 29-86 564 94 342 SCL 0.27 1.28
Bt1 86-110 564 54 382 SC 0.14 1.42
Bt2 110-180 564 54 382 SC 0.14 1.48
Mean 592 102 306 0.50 1.32
CV 10.63 49.22 43.11 88.51 9.75
Aliba et al. NJSS 30 (1) 2020 111-123
118
occasioned by the humid tropical conditions prevalent in
the area which encourages rapid losses of organic matter.
The decrease of organic matter values with soil depth in
all the pedons probably might be due to decreased floral
and faunal activities in the underlying horizons, as sug-
gested by Browaldh (1995). Total nitrogen (TN) of the
soils generally followed a decreasing trend like organic
matter. In the east lying slope, mean TN varied from 1.26-
1.43 g kg-1, while in the west-lying slope, it ranged from
1.10-1.36 g kg-1. According to Havlin et al. (2012), TN of
the soils is considered generally low when values are < 1.5
g kg_1. Thus, the two slopes under study were low in TN
and may be due to the low organic matter content of the
soil since total nitrogen is associated with organic matter
fraction of the soils (Brady and Weil, 2016).
The exchangeable bases were higher in the west lying
toposequence relative to the east lying toposequence. In
Umudike east-lying slope, total exchangeable bases (TEB)
ranged from 7.3-12.2 cmol kg-1 whereas, in Itu west lying
slope, it varied from 8.919-14.336 cmol kg-1. Exchangea-
ble bases were higher in the footslope and midslope of east
and west lying slopes, respectively (Table 6 and 7). Also,
low variability in the distribution of TEB was observed at
the summit and footslope of the east lying slope, whereas
its distribution varied highly (CV > 35%) at the midslope.
This may be due to the effect of slope percentage, which
might have resulted in an unstable distribution of basic
cations at this soil position. However, the total base satura-
tion of Itu west-lying slope showed moderate variation in
distribution except for footslope that had more homogenei-
ty in distribution evident in the low variability recorded
(Table 7). Cation exchange capacity (CEC) of both
toposequences studied did not follow any particular trend
down the profile and slope. However, on a mean value
basis, in Umudike east lying slope, its abundance across
the topo units was in the order of footslope (13.79 cmol kg-1) > summit (10.06 cmol kg-1) > midslope (8.63 cmol kg-1)
while in the Itu west lying slope, the order of abundance
was midslope (16.31 cmol kg-1) > footslope (15.77 cmol
kg-1) > summit (10.42 cmol kg-1). According to the rating
of CEC given by Landon (1996) (in cmol kg-1) where > 40
very high, 25-40 high, 15-25 medium, 5-15 low. Therefore
it can be inferred that except for midslope and foot slope
of Itu west lying toposequences which attained medium
CEC level, the other topo units studied had low CEC. The
low CEC of these soils indicates the low capacity of these
soils to retain nutrient elements. Low cation exchange
capacity, which might be as a result of low clay and organ-
ic matter contents of the soils, may render soils unsuitable
for intensive agriculture (Kparmwang et al., 2004). For
the Percentage base saturation (% BS) of the soils, mean
values of 87.76, 82.44 and 86.33 % were noted in the
summit midslope and footslope of the Umudike east-lying
slope (Table 6) while in Itu west-lying slope, average val-
ues of 85.51, 87.50 and 90.76 % were recorded for the
summit, midslope and footslope, respectively (Table 7).
The high mean values of % BS values recorded for the top
units in this present study which were above the recom-
mended 80% limit to be maintained in most cropping sys-
tems (Hodges, 2002) indicated that top units when proper-
ly managed could be highly productive. Low variability
(CV ≤15%) recorded for % BS in all the pedons studied
indicated homogeneity of this soil property across soil
depths.
3.4. Classification of the Pedons of the Two Toposequenc-
es of Varying Orientations
The soils of the pedons dug at the topo units of the east,
and west lying toposequences were classified according to
the USDA Soil Taxonomy System (Soil Survey Staff,
2010) and then correlated with World Reference Base for
Resources (IUSS Working Group WRB, 2010). The dif-
fering soil physical, chemical and morphological proper-
ties formed the basis for the classification. The pedon dug
at the Umudike east lying summit has a clay bulge indicat-
ing argillation and was sandier than all other top units with
the mean sand value of 666.8 g kg-1. At the same time, the
organic carbon decreased consistently with depth and
meant the base saturation value of 87.76 % observed. Con-
sequently, at the order level, the pedon was classified as
Alfisol (Table 8). Due to the Udic moisture regime and 7.5
YR with chroma of 5-8 at the lower horizons observed, the
pedon was classified as Udalf and Paleudalf at the subor-
der and subgroup levels, respectively. In contrast, at the
Great group level, the pedon was classified as Grossarenic
Paleudalfs since there is the presence of sandy particle size
throughout the argillic horizon of the profile. Investigation
of the pedon dug at the midslope of the Umudike east ly-
ing slope showed prominent clay bulge, a consistent de-
crease in organic matter with soil depth, high base satura-
tion, udic moisture regime and chroma value of 6-8. Based
on these findings, the pedon was classified as Alfisol,
Udalf, Paleudalf and Typic Paleudalf at the order, subor-
der, subgroup and great group levels, respectively (Table
8). Examination of footslope pedon of the Umudike east
lying slope indicated the presence of clay bulge with the
apex at the Bt1 and Bt 2 horizons, high percentage base
saturation, low organic matter which consistently de-
creased with soil depth, Udic moisture regime and domi-
nance of sandy particle size class throughout the horizon
extending from the mineral soil surface to the top of the
argillic horizon to a depth of 50 cm. Consequently, at the
order and suborder levels, the pedon was classified as al-
fisol and Udalf, respectively. In contrast, at the subgroup
and great group levels, the pedon was classified as Kan-
didalf and Arenic Kandidalf, respectively (Table 8).
The Itu west lying summit was classified as Alfisol at the
order level since there is pronounced presence of clay
bulge with a mean sand value of 662.8 g kg-1 and high
base saturation. At the suborder level, the pedon was clas-
sified as Udalf due to the observation of Udic moisture
regime. However, at the subgroup and great group levels,
the pedon was classified as Glossudalf and Arenic Glossu-
dalf due to the presence of glossic horizon and sandy parti-
cle size class throughout a horizon which extended from
the mineral soil surface to the top of an argillic horizon up
to a depth of 50 cm. Investigation of the pedon dug at the
midslope of the Itu west lying slope indicated distinct clay
bulge, low organic matter level which decreased with
depth, high base saturation, udic moisture regime and
chroma of 6-8. Guided by these findings, the pedon was
classified as Alfisol and Udalf at order and suborder levels
Classification and Fertility Status of Soils on Slopes of Varying Orientations
119
Table 6: Chemical properties of the east-lying toposequence
Key: OM= organic matter, TN=total nitrogen, TEB=total exchangeable bases, CEC= cation exchange capacity, %BS=percentage base saturation.
Table 7: Chemical properties of the west-lying toposequence
Key: OM= organic matter, TN=total nitrogen, TEB=total exchangeable bases, CEC= cation exchange capacity, %BS=percentage base saturation
Horizon Depth
(cm)
pH
(H20)
OM
(gkg-1)
TN
(gkg-1)
Ca
Mg K
Na
(Cmolkg-1)
TEB
CEC %BS
Umudike East-Lying Summit (Grossarenic Paleudalfs)
A 0-5 4.5 40 2.3 5.2 4.8 0.132 0.417 10.549 11.75 89.78
AB 5-23 4.4 29.3 1.4 5.2 1.6 0.065 0.348 7.213 8.41 85.77
Bt1 23-56 4.7 20 0.98 5.6 3.2 0.039 0.356 9.195 10.56 87.07
Bt2 56-95 4.8 17.8 0.91 6 2.4 0.049 0.478 8.927 9.97 89.53
Bt3 95-130 4.8 9.2 0.7 4.8 3.2 0.042 0.304 8.346 9.63 86.67
Mean 4.64 23.26 1.26 5.36 3.04 0.065 0.381 8.846 10.06 87.76
CV 3.92 50.63 50.52 8.51 39.03 58.969 17.795 13.782 12.19 2.06
Umudike East-Lying Midslope (Typic Paleudalfs)
A 0-7 4.6 42.3 2.4 5.6 1.6 0.107 0.304 7.611 8.81 86.39
AB 7-37 4.8 38.4 1.68 5.2 3.6 0.08 0.461 9.341 10.7 87.30
Bt1 37-66 4.6 31.5 1.4 4.4 3.6 0.137 0.478 8.615 9.9 87.02
Bt2 66-100 4.9 12.6 0.98 2 0.4 0.047 0.339 2.786 4.23 65.86
Bt3 100-150 5 7.4 0.7 4 3.6 0.05 0.495 8.145 9.51 85.65
Mean 4.78 26.44 1.43 4.24 2.56 0.084 0.415 7.300 8.63 82.44
CV 3.74 59.03 46.05 33.09 58.04 45.53 21.049 35.646 29.58 11.13
Umudike East-Lying Footslope (Arenic Hapludalfs)
A 0-7 4.2 44.8 2.56 4.8 3.6 0.141 0.33 8.871 10.07 88.09
AB 7-20 4.4 31 1.4 5.2 1.6 0.076 0.365 7.241 8.76 82.66
Bt1 20-52 4.8 25.9 1 4 2.8 0.046 0.391 7.237 8.68 83.38
Bt2 52-98 4.7 20.6 0.91 21.2 6 0.089 0.461 27.75 29.65 93.59
Bt3 98-150 4.8 9.8 0.7 7.6 2 0.032 0.269 9.901 11.8 83.91
Mean 4.58 26.42 1.31 8.56 3.2 0.077 0.363 12.2 13.79 86.33
CV 5.86 48.96 56.42 84.02 54.49 55.345 19.622 71.855 64.93 5.30
Horizon
DEPTH
(cm)
pH
(H2O)
OM
(g kg-1)
TN
(g kg-1)
Ca
Mg K Na TEB
(Cmolkg-1)
CEC %BS
Itu West-Lying Summit (Arenic Glossudalfs)
A 0-6 5.3 42.4 2.1 5.2 1.6 0.127 0.443 7.37 8.73 84.42
AB 6-38 5.8 25.3 1.4 5.4 2.6 0.063 0.321 8.384 9.74 86.08
Bt1 38-83 5.9 12.6 0.98 7.2 1.2 0.039 0.495 8.934 10.53 84.84
Bt2 83-106 5 9.2 0.56 8.4 3.6 0.029 0.304 12.333 13.61 92.50
Bt3 106-120 4.5 5 0.44 5.2 2 0.033 0.343 7.576 9.5 79.75
Mean 5.3 18.9 1.10 6.28 2.2 0.058 0.381 8.919 10.42 85.51
CV 10.921 80.251 61.74 23.141 42.64 69.862 21.875 22.524 18.17
6 4.545
Itu West-Lying Midslope (Typic Paleudalfs)
A 0-7 4.5 43.6 2.24 12.8 7.6 0.153 0.374 20.927 22.27 93.97
AB 7-26 4.6 38 1.48 9.2 2 0.133 0.391 11.724 13.4 88.35
Bt1 26-50 4.7 31.5 1.12 6.8 4.8 0.052 0.452 12.104 13.95 86.77
Bt2 50-73 4.8 24.1 1.1 10 4 0.06 0.522 14.582 16.5 88.38
Bt3 73-110 4.8 16 0.84 8.2 3.6 0.064 0.478 12.342 15.42 80.04
Mean 4.68 30.64 1.36 9.4 4.4 0.092 0.443 14.336 16.31 87.50
CV 10.921 80.251 61.74 23.141 42.64 69.862 21.875 22.524 18.17
6 4.545
Itu West-Lying Footslope (Typic Ferrudalfs)
A 0-8 4 44.8 1.98 8.8 5.2 0.094 0.408 14.502 15.78 91.90
AB 8-29 4.5 36.2 1.12 7.2 4.4 0.057 0.495 12.152 13.83 87.87
BA 29-86 4.6 24.7 0.98 13.2 6.8 0.07 0.522 20.592 22.36 92.09
Bt1 86-110 4.6 17.6 0.84 8.2 3.6 0.045 0.452 12.297 12.66 97.13
Bt2 110-180 4.9 7.2 0.56 8.4 3.2 0.062 0.382 12.044 14.2 84.81
Mean 4.52 26.1 1.10 9.16 4.64 0.066 0.452 14.317 15.77 90.76
CV 7.237 56.93 48.887 25.481 30.842 27.872 12.899 25.506 24.42
8 3.373
Aliba et al. NJSS 30 (1) 2020 111-123
120
of classification. In contrast, at the subgroup and great
group levels, the pedon was classified and Paleudalf and
Typic Paleudalf, respectively (Table 8). Pedon dug at the
Itu west lying footslope was classified as Alfisol at the
order level due to the prominent presence of argillic hori-
zon, low organic matter which consistently decreased with
soil depth. However, the pedon was classified as Udalf and
Ferrudalf at the suborder and subgroup levels, since Udic
moisture regime and chroma of 2 up to a depth of 86 cm
were observed. At the great group level, the pedon was
classified as Typic ferrudalf, since other conditions like
mottles were not prominent at that depth. When correlated
with the world reference base at this level, the pedon was
classified as Haplic Albeluvisols (Table 8).
3.5Fertility Status of the Two Toposequences of Varying
Orientations using Elemental Ratios
Using Ca/Mg and K/Mg elemental ratios, the fertility sta-
tus of the Umudike east lying toposequence and Itu west
lying toposequence were assessed and the findings pre-
sented in Tables 9 and 10. The results showed that at the
Umudike East lying toposequence, mean Ca/Mg values of
2.01, 2.45 and 2.66 were observed for the summit, mid-
slope and footslope, respectively while at the Itu west ly-
ing toposequence, mean values of 3.25, 2.49 and 2.03
were recorded for the summit, midslope and footslope.
Johnstone (2011) had earlier asserted that the Ca/Mg ratio
of fertile soils is usually in the range of 3:1-7:1. Also, Lan-
Table 8: Classification of the soils of the east and west lying toposequences
Location USDA Soil Taxonomy System
(Soil Survey staff 2010)
World Reference Base, 2010
UELS Grossarenic Paleudalfs Mollic Luvisols
UELMS Typic Paleudalfs Mollic Luvisols
UELFS Arenic Hapludalfs Mollic Luvisols
IWLS Arenic Glossudalfs Haplic Albeluvisols
IWLMS Typic Paleudalfs Haplic Albeluvisols
IWLFS Typic Ferrudalfs Haplic Albeluvisols
Key UELS; Umudike East Lying summit, UELMS: Umudike East Lying midslope
UELFS: Umudike East Lying Footslope, IWLS: Itu West Lying Summit
IWLMS: Itu West Lying Midslope, IWLFS: Itu West Lying Footslope
don (1991) reported that the Ca/Mg ratio of less than 3:1 is
typical of unfertile soils. Going by the assertions above,
only the summit of the Itu west lying toposquence could
be considered fertile while the other top units were of re-
duced fertility. The very low Ca/Mg observed in the ma-
jority of the pedons indicated possible Ca deficiency and
inhibition of P uptake in the soils (Udo et al., 2009).
K/Mg ratio of the soils of the two toposequences varied
across the top units and slope orientation. At the Umudike
east, lying toposequence, values ranging from 0.01-0.04,
0.01-0.07, 0.01-0.05 were noted for the summit, midslope
and footslope, respectively (Table 9). However, at the Itu
west lying toposequence, values in the range of 0.01-0.08
were observed at the summit, 0.01-0.07 at the midslope
while 0.01-0.02 was noted at the footslope (Table 10). It
has been reported that ideal K/Mg ratio in the fertile soils
is in the range of 0.2-.0.35 and K/Mg ratio greater than 2:1
may inhibit the uptake of Mg (Udo et al., 2009). Conse-
quently, the pedons of the two toposequences of varying
orientations were considered infertile. However, inhibition
of Mg uptake is not expected in the soils. Generally, there
was no well-defined pattern of distribution of the K/Mg
ratio in the soils and high variation in distribution was
observed.
4.0. Conclusion
The findings of this study showed that the soils of the two
toposequences of varying orientation were highly weath-
ered and dominated by sandy clay loam texture. Bulk den-
sity values in the east and west slopes were adequate for
agricultural production. The soils of the two toposequenc-
es were acidic. Organic matter in both toposequences was
generally low likewise total nitrogen. There was a clear
dominance of Calcium in total basic cations of the soils,
especially at the foot slopes. The Ca/Mg, and K/Mg ratios
were higher at midslope and foot slope of east lying slope
whereas, the reverse was the case in west lying slope
where high values were recorded in summit and midslope.
Classification and fertility status of soils on slopes of varying orientations
121
Table 9: Selected fertility indices of the east-lying toposequence
Horizon Depth (cm) Ca/Mg K/Mg
Umudike East-lying summit
A 0 -5 1.08 0.03
AB 5-23 3.25 0.04
Bt1 23-56 1.75 0.01
Bt2 56-95 2.5 0.02
Bt3 95-130 1.5 0.01
Mean 2.016 0.022
CV 42.743 59.265
Umudike East-lying midslope A 0-7 3.5 0.07
AB 7-37 1.44 0.02
Bt1 37-66 1.22 0.04
Bt2 66-100 5 0.12
Bt3 100-150 1.11 0.01
Mean 2.454 0.052
CV 70.385 85.355
Umudike East-lying footslope
A 0-7 1.33 0.04
AB 7-20 3.25 0.05
Bt1 20-52 1.43 0.02
Bt2 52-98 3.53 0.01
Bt3 98-150 3.8 0.02
Mean 2.668 0.028
CV 44.688 58.685
C/N = Carbon-nitrogen ratio,Ca/Mg = Calcium-magnesium ratio,K/Mg = Potassium –magnesium ratio, CV= Coefficient of variation.
Table 10: Selected fertility indices of the west-lying toposequence
Horizon Depth Ca/Mg K/Mg
Itu West-lying summit A 0-6 3.25 0.08 AB 6-38 2.08 0.02 Bt1 38-83 6 0.03 Bt2 83-106 2.33 0.01 Bt3 106-120 2.6 0.02 Mean 3.252 0.032 CV 43.921 76.594
Itu West-lying midslope A 0-7 1.68 0.02 AB 7-26 4.6 0.07 Bt1 26-50 1.42 0.01 Bt2 50-73 2.5 0.02 Bt3 73-110 2.28 0.02 Mean 2.496 0.028 CV 44.962 76.594
Itu West-lying footslope A 0-8 1.69 0.02 AB 8-29 1.64 0.01 BA 29-86 1.94 0.01 Bt1 86-110 2.28 0.01 Bt2 110-180 2.63 0.02 Mean 2.036 0.014 CV 20.519 39.123
Key: Ca/Mg = Calcium-Magnessium ratio, K/Mg = Potassium –Magnesium ratio, CV= Coefficient of variation.
It can, therefore, be inferred that slope angle and orienta-
tion of these toposequencies played a prominent role in
regulating these fertility indices. The pedons of the sum-
mit, midslope and footslope were as classified Grossarenic
Paleudalfs, Typic Paleudalfs and Arenic Hapludalfs, re-
spectively for the east-lying slope and Arenic Glossudalfs,
Typic Paleudalfs and Typic Ferrudalfs, respectively for the
west-lying slope. Generally, regardless of the influence of
Aliba et al. NJSS 30 (1) 2020 111-123
122
top units and slope orientation, the two toposequences
were of poor fertility status.
References
Abe S.S, Oyediran G.O, Masunaga T, Yamamoto S, Hon-
na T, and Wakatsuki T (2009). Soil development and
fertility characteristics of inland valleys in the rain forest
zone of Nigeria: Mineralogical composition and particle
-size distribution. Pedosphere, 19:505-514.
Aduloju, M. O. and Tetengi, M. (2011). Physico-chemical
properties of soils in a toposequence in Mokwa, Niger
State, Nigeria. Crop Res. 42 (1, 2 & 3) : 144-147 (2011)
Printed in India.
.Akinbola, G. E., Ojo U. A., and Adigun, M. O. (2009).
Variability of properties of some pedons on basement
complex of southwestern Nigeria, Proceedings of the
34th annual conference of the soil science society of
Nigeria. March 22nd -26th, 2010 Ibadan, Nigeria.
Annan-Afful E, Iwashima N, Otoo E, Asubonteng K.O,
Kubota D, Kamidohzono A, Masu M.T, Wakatsuki, T
(2004). Nutrient and bulk density characteristics of soil
profiles in six land use systems along topo-sequences in
inland valley watersheds of Ashanti region, Ghana. Soil
Sci. Plant Nutr. 50:649-664.
Birkeland, P. W. (1984). Soils and Geomorphology. Ox-
ford University Press, NY. Pp 448.
Brady, N. C. and Weil, R. R. (2004). The nature and prop-
erties of soils, 12th ed. Delhi: Pearson Education.
Brady, N.C. and Weil, R.R. (2010). Elements of the nature
and properties of soils. 3rd Edition. Prentice-Hall, Upper
Saddle River, NJ.
Bremner, J.M. and Mulvaney, G.S. (1982). Total Nitrogen.
In: Page, A.L., Miller, R.H. and Keeney, D.R. (Eds) Part
2 Vol. 9. Methods of soil analysis.American Society of
Agronomy. Madison, Wisconsin. Pp 595- 624.
Browaldh, M. (1995). The influence of trees on nitrogen
dynamics in an agrisilvicultural system in Sweden. Ag-
roforestry System, 30(3): 301-313.
Buol, S.W., Hole, F.D., McCracken, R.J. and Southard,
R.J., (1997). Soil Genesis and Classification, 4th edition.
Iowa State Univ. Press, Ames, IA.
Chukwu, G.O. (2013). Soil survey and classification of
Ikwuano Abia state, Nigeria. J. of Environ. Sci. and Wa-
ter Resour., 2 (5): 150 – 156.
Cools, N, and De Vos B (2010). Sampling and analysis of
soil. Manual part X, 208 pp. In: Manual on methods and
criteria for harmonized sampling, assessment, monitor-
ing and analysis of the effects of air pollution on forests,
UNECE, ICP Forests, Hamburg. ISBN: 978-3-926301-
03-1. [http://www.icp-forests.org/Manual.htm].
Esu I. E. (2010). Soil characterization, classification and
survey. HEBN Publishers, Plc, Ibadan, Nigeria, 232pp.
Esu, I.E. A.U. Akpan-Idiok and M.O. Eyong. (2008) Char-
acterization and Classification of soils along a typical
Hillslope in Afikpo Area of Ebonyi State, Nigeria. Nige-
rian Journal of Soil and Environment, vol. 8, pp. 1-6,
2008.
FAO (Food and Agricultural Organization) (2004). A Pro-
visional methodology for land degradation assess-
ment.Food and Agricultural Organization, Rome.
FAO (Food and Agriculture Organization) (1998) World
Reference Base for soil resources 84 World Resources
Report. Food and agriculture the Intervention Organiza-
tion Rome 1998.
Gee, G. and Or D. (2002) Particle size distribution: In
Dane J.H., Topp G.C. (eds). Methods of soil analysis
Part 4 Physical methods. Soil Sci. Soc. Am Book series
No. 5 ASA and SSSA, Madison WI 2002; 225-293.
Havlin, J.L., Beaton, J.D., Tisdale, S.L. and Nelson, W.L.
(2012). Soil fertility and fertilizers. An introduction to
nutrient management.7th ed. PHI Private Limited, New
Delhi-110001. Pp 513.
Iqbal J., Read J.J., Thomasson A.J. and Jenkins J.N.
(2004): Relationships between soil-landscape and dry-
land cotton lint yield. Soil Sci. Soc. Am. J., 69: 1–11.
IUSS Working Group WRB. (, 2010). Addendum to the
World Reference Base for Soil Resources: Guidelines
for constructing small-scale map legends using the
World Reference Base for Soil Resources. FAO, Rome.
Johnston, J. (2011). Assessing soil fertility; the importance
of soil analysis and its interpretation. Potash develop-
ment association pp19.
Kalivas, D.P. Triantakonstantis, D.P. and Kollias. V.J.
(2002) "Spatial prediction of two soil properties using
topographic information". Global Nest: the Int. J. vol. 4,
no. 1, pp. 41-49, 2002.
Kparmwang, T., Chude, V.O. and Abdullahi, D. (2004).
The classification and genesis of benchmark soils of
Bauchi State, Nigeria. Journal of Soil Science,14: 30-39.
Landon, J.R. (1991). Brooker tropical Soil manual: A
handbook for Soil Survey and agricultural land evalua-
tion in the tropics and subtropics, Essex. Addison Wes-
ley Loghan Ltd. Pp 472.
Landon, J.R. (1996). Soil chemistry. Booker tropical soil
manual. Longman England.
Moradi S (2013). Impacts of organic carbon on consisten-
cy limits in different soil textures. Int. J. Agric. Crop
Sci. 5(12): 1381-1388.
Mulla, D.J. and McBratney, A.B. (2001). Soil spatial vari-
ability, pp. 343-374. In A.W. Warrick (ed.). Soil Physics
Companion. CRC Press. The USA.
Nelson.D.W. and Sommers, L.E. (1982). Phosphorus. In:
page, A.L., Miller, R.H. and Keeney, D.R. (Eds). Meth-
ods of soil analysis Part 2. Ameri. Soc. Agron. Madison,
Wisconsin. Pp. 539 -579.
NIMET (2008). Nigeria Climate Review Bulletin 2007.
Nigerian Meteorological Agency. NIMET-No. 001.7.
Classification and fertility status of soils on slopes of varying orientations
123
Nuga, B.O., Eluwa, N.C and Akinbola.G.E. (2006). Char-
acterization and classification of soils along a
toposequence in Ikwuano Local Government Area of
Abia State Nigeria. Electronic Journal of Environmen-
tal, Agricultural and Food Chemistry. ISSN: 1579-4377.
Obi, J. C. (2015). Particle size fractions and pedogenesis
of coastal plain sands. Archives of Agronomy and Soil
Science 61(10): 1473–1490
Obi, M.E. (1982). Runoff and soil loss from an oxisol in
SouthEastern Nigeria under various management prac-
tices. Agric. Water Management, 5:193-203.
Ogban, P.I. O. Babalola and A.M Okoji. (1999). "Profile
Characteristics of a typical toposequence in Southern
Nigeria". Africa Soils, vol. 28, pp. 147–165, 1999.
Onweremadu, E.U. (2006). Application of geographic
information system (GIs) on soil land use and soil-
related environmental problems in southeastern Nigeria.
A Ph.D Thesis of the University of Nigeria, Nuskka,
Nigeria 2006, 33 pp.
Orajaka, S. O. (1975). Geology. In Nigeria in maps: East-
ern States. G. E. K. Ofomata (Ed.) Ethiope publishing
house, Benin City, Nigeria.
Osodeke, V. E. and Osondu. N.E. (2006) "Phosphorus
distribution along a toposequence of a coastal sand par-
ent material in southeastern Nigeria". Agricultural J.,
vol. 1, no. 3, pp. 167-171, 2006.
Osodeke, V.E., Nwotiti, I.L. and Nuga, B.O. (2005).
"Sesquioxides distribution along a toposequence in
Umudike area of southeastern Nigeria". Electronic J. of
Environmental, Agricultural and Food Chemistry, vol.
4, no. 61, pp. 117-1124, 2005.
Peterschmitt, E., Fritch, E., Rajot, J.L., Herbillon, A.J.,
( 1996) Yellowing, bleaching and fertilization processes
in soil mantle of the Western Ghats, south India. Ge-
oderma 74:235 – 253.
Soil Survey Staff, (2010). Keys to Soil Taxonomy. 11th
Edn., United States Department of Agriculture, Natural
Resources Conservation Service, Washington DC.,
U.S.A.
Sombroek, W.G., and Zonneveld, I.S. (1971). Ancient
dune fields and fluviatile deposits in the Rima-Sokoto
River Basin (NW Nigeria). A soil Survey paper, No. 5.
Soil Survey Inst. Wageningen, the Netherlands, 109 pp.
Southeastern Nigeria. East Africa Agricultural and For-
estry Journal, 48: 81–91.
Thomas G.W. (1996). Soil pH and soil acidity. In: Sparks
D.L, Page A.L., Helmke P.A., Loeppert R.H.,
Soltanpour P.N., Tabatabai M.A., Johnson C.T. and
Summer M.E. (Eds.). Methods of Soil Analysis, Part 3.
Chemical Methods. Soil Science Society of America,
Inc, and American Society of Agronomy, Maidson,
WI.The USA. Pp475-49.
Thomas, G.W. (1982). Exchangeable Cation. In A.L. Page
R.H. Miller and D.R Ikeeny (eds). Method of Soil Anal-
ysis Part 2.2nd Edition. Am. Soc. Of Agron. Madison,
Pp 22-27.
Udo, E.J., Ibia, T.O., Ogunwale, J.A., Ano, A.O. and Esu,
I.E. (2009). Manual of soil-plant and water analyses.
Sibon Book limited, Festac Lagos. Pp. 183.
Wilding L.P., J. Bouma, and D.W. Boss. (1994). Impact of
Spatial Variability on Interpretative Modelling. In: Bry-
ant R.B. and R.W. Arnold- Quantitative Modeling of
Soil Forming Process. SSSA Special Publ., No. 39: 61-
75.
Zinck, A. (1993). Soil Survey: An epistemology of a vital
discipline ITC. Journal 1990, 4: 335-350. Soil Survey
Division Staff. 1993. Soil Survey Manual. Soil Conser-
vation Service.
Aliba et al. NJSS 30 (1) 2020 111-123